Influence of light curing source on microhardness of composite resins of different shades

André Luiz Fraga Briso,Sílvio José Mauro,Tânia Maria Fedel,Sibéria De Morais Pereira,Maria Lúcia Marçal Mazza Sundefeld,Renato Herman Sundfeld

doi:10.1590/s1678-77572006000100003

André Luiz Fraga Briso, Sílvio José Mauro + Show 4 more

Open Access

https://doi.org/10.1590/s1678-77572006000100003

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Abstract

Introduction:The evolution of light curing units can be noticed by the different systems recently introduced. The technology of LED units promises longer lifetime, without heating and with production of specific light for activation of camphorquinone. However, further studies are still required to check the real curing effectiveness of these units.Purpose:This study evaluated the microhardness of 4 shades (B-0.5, B-1, B-2 and B-3) of composite resin Filtek Z-250 (3M ESPE) after light curing with 4 light sources, being one halogen (Ultralux – Dabi Atlante) and three LED (Ultraled – Dabi Atlante, Ultrablue – DMC and Elipar Freelight – 3M ESPE).Methods:192 specimens were distributed into 16 groups, and materials were inserted in a single increment in cylindrical templates measuring 4mm x 4mm and light cured as recommended by the manufacturer. Then, they were submitted to microhardness test on the top and bottom aspects of the cylinders.Results:The hardness values achieved were submitted to analysis of variance and to Tukey test at 5% confidence level. It was observed that microhardness of specimens varied according to the shade of the material and light sources employed. The LED appliance emitting greater light intensity provided the highest hardness values with shade B-0.5, allowing the best curing. On the other hand, appliances with low light intensity were the least effective. It was also observed that the bottom of specimens was more sensitive to changes in shade.Conclusion:Light intensity of LED light curing units is fundamental for their good functioning, especially when applied in resins with darker shades.

Highlights

The lowest values were achieved with the Ultrablue unit (DMC), whereas the Ultralux (Dabi Atlante) and Ultraled units (Dabi Atlante), respectively, presented intermediate results (Tables 2)
When the composite resin shades were considered at the top surfaces, groups of B-0.5 shade presented highest hardness values, whereas other shades presented similar results
With regard to the appliances analyzed in the present study, halogen light unit is the most widely employed and, because it works in a wider light spectrum, besides curing the restorative material, it may heat the tooth and composite resin during the process[23]

Summary

Introduction

Curing depth is often considered a primary factor for clinical success of composite resin restorations, since it directly affects the physical properties of materials and longevity of restorations. The factors that may affect the curing of resin materials according to the literature[7,17,25,28] include those directly related to the restorative material, including composite resin shade, amount of photoinitiators, organic and filler matrixes. In an attempt to optimize the utilization of light cured composites, manufacturers of light curing units have developed different curing systems, including those with soft start mechanism, which gradually increase light intensity, and those that emit a constant light intensity higher than 1,000mW/cm[2]. Light emitting diode (LED) light curing units were developed, which apply a lower light intensity than conventional light curing units, yet are able to cure resin materials, because of light emission in specific wavelength for activation of camphorquinone (450 to 480nm)[10,14]

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